Heat developable photosensitive materials which utilize silver halides as a photosensitive component are well-known in the field of this art, and described, e.g., in Shashin Koqaku no Kiso (which means fundamentals of photographic engineering), volume "Higinen Shashin" (which means "Nonsilver Photography"), pages 242 to 255, Corona Co. (1982); Eizo Jouho (which means image information), page 40 (April 1978); Nebletts, Handbook of Photography and Reprography, 7th Ed., pages 32 to 33, Van Norstrand Reinhold Company; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075; British Patents 1,131,108 and 1,167,777; and Research Disclosure (which is abbreviated as RD, hereinafter), pages 9 to 15 (June 1978).
Many methods for forming color images through heat development have been proposed.
For instance, methods of forming color images by binding couplers to the oxidation product of the developing agents which are produced through the reduction of silver halides are disclosed in U.S. Pat. Nos. 3,531,286, 3,761,270 and 4,021,240; Belgian Patent 802,519, RD-13742, and so on.
In addition, methods of forming positive dye images through heat development according to the silver dye bleach process utilizing silver halides are disclosed in U.S. Pat. No. 4,235,957, RD-14433, RD-15227, and so on.
Moreover, there have been proposed methods comprising a step of imagewise forming or releasing diffusible dyes from dye-providing compounds in accompanied with the heat development of silver halides, and a step of transferring the formed or released diffusible dyes into a mordant-containing dye-fixing element with the aid of a solvent such as water or the like, into a dye-fixing element using a high boiling organic solvent or a hydrophilic thermal solvent incorporated in the dye-fixing element, or into a dye-receiving element such as a support or so on when the mobility of the dyes originates from thermal diffusibility or sublimability. In those methods, either dye image, negative or positive to original ones, can be obtained by changing dye-providing compounds and/or silver halides to be used in kind (as disclosed in U.S. Pat. Nos. 4,463,079, 4,474,867, 4,478,927, 4,507,380, 4,500,626 and 4,483,914, JP-A-58-149046 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-58-149047, JP-A-59-152440, JP-A-59-154445, JP-A-59-165054, JP-A-59- 180548, JP-A-59-168439, JP-A-59-174832, JP-A-59-174833, JP-A- 59-174834, JP-A-59-174835, JP-A-62-65038, JP-A-61-23245, EP-A-210660, EP-A-220746, and so on).
However, the above-described heat developable photosensitive materials are development-processed under heating to high temperatures, so they have generated fog (or lowering of Dmax in photosensitive materials of the kind which make a positive response to a positive original) to a considerable extent, in contrast to ordinary photosensitive materials to undergo development-processing in the vicinity of room temperature. That is, They have been hard to provide photographs excellent in image distinguishability (with high S/N).
Although hydroxytetrazaindenes, benzotriazoles and the like are known to be effective as antifoggant in ordinary photosensitive materials to be developed in the vicinity of room temperature, they have failed in achieving the end desired and, what is worse, have caused a lowering of sensitivity when applied to heat developable photosensitive materials.
Also, the desired end has not been achieved with antifoggant-containing heat developable photosensitive materials disclosed in JP-A-59-168442, JP-A-59-111636, JP-A-59-177550, JP-A-60-168545, JP-A-60-180199, JP-A-60-180563, JP-A-61-53633, JP-A-62-78554, JP-A-62-123456, JP-A-63-133144, and so on.